1. Field of the Invention
The present invention relates to a lamination type magneto-resistive head used for a magnetic recording/reproducing apparatus.
Recently, a magneto-resistive head has come to attract the attention in compliance with the trend to a higher recording density, higher data transfer speed and multi-channel recording in the magnetic recording/reproducing apparatus. Especially, with the magnetic recording/reproducing apparatus in which a magnetic recording medium runs at a low speed, magneto-resistive heads are being used so that the reproduced outputs are independent of the speed.
2. Description of the Prior Art
FIG. 6(a) and 6(b) show a conventional magneto-resistive head. FIG. 6(a) is a perspective view of the main area and FIG. 6(b) is a sectional drawing shown at a section I--I' of FIG. 6(a). The conventional magneto-resistive head is formed with a first magnetic layer 27 composed of Permalloy, Sendust or amorphous magnetic materials, etc. on a substrate 21 which is comprised of glass or ceramics, a bias conductor 22 composed of a conductive material such as gold thin film or copper thin film which is a means of applying a bias magnetic field to a magneto-resistive element 23, a magneto-resistive element 23 comprised of Permalloy thin film, electrodes 24a and 24b formed of the gold thin film or copper thin film for providing a driving current to the magneto-resistive element 23, a second magnetic layer 25 and a third magnetic layer 26 composed of soft magnetic material through an insulating layer 32 such as SiO.sub.2 or the like together with a first gap 28 and a second gap 29 consecutively. Furthermore, a protection layer 31 is formed and finally a cover plate 3 is bonded, thereby completing the magneto-resistive head. In the vicinity of the second gap 29, between the second magnetic layer 25 and the third magnetic layer 26, said magneto-resistive element 23 is formed in such a manner that said magneto-resistive element 23 over-laps each edge of the second magnetic layer 25 and the third magnetic layer 26. Likewise, the first gap 28 which conducts into the magnetic head a recording magnetic field generated from a magnetic recording medium is formed between the first and second magnetic layers 27 and 25. The surface 33 is the sliding surface of magnetic medium.
Recently, such a magnetic head is desired that enables a plurality of track formats having a different track width to be conformed. However, it has been impossible for the above-mentioned conventional magnetic head to conform to a plurality of track formats which allow reproduction at almost the same position of the magnetic recording medium having a different track width.
In order to conform to such demand, a lamination type magneto-resistive head 80 as shown in FIG. 7 is known. This is the same structure as that of the conventional example, and the first magneto-resistive type head 81a and the second magneto-resistive type head 81b which are different in track width from each other are consecutively laminated on a common substrate through a separate layer 83 so that the second magnetic gap 29a of the first magneto-resistive head 81a faces the first magnetic layer 27b of the second magneto-resistive type head 81b. In such a case, each magneto-resistive head has a different reproducing track width, allowing a plurality of track formats having a different track width to be conformed. That is, the magneto-resistive head 81b is used for the one track format, while the head 81a is used for another track format.
However, as mentioned above, the magneto-resistive element 23a on the first magneto-resistive type head 81a faces with the first magnetic layer 27b of the second magneto-resistive type head 81b, and the first magnetic layer 27b of the second magneto-resistive type head 81b acts as a magnetic shield with respect to the first magneto-resistive head, thereby preventing-the signal magnetic field generated from the magnetic recording medium from flowing into the first magneto-resistive head. Therefore, there has been a problem in that a reproducing sensitivity is lowered at an area where 1/2 of the recorded wavelength on the magnetic recording medium is larger than a distance L between the first gap 28a of the first magneto-resistive head 81a and the first magnetic layer 27b of the second magneto-resistive head 81b.